Recently, the above mentioned electronic devices have increasingly been made more compact, more lightweight, and thinner, as well as achieving more advanced performance. Accordingly, various heat-generating elements installed therein dissipate a larger amount of heat. To make the electronic device itself more compact, more lightweight, and thinner, a similar function is also required as a cooling device. In general, such electronic devices are cooled by a built-in heat pipe having a superior apparent thermal conductivity against metals, such as copper, aluminum, etc. The heat pipe itself, however, also has to be more compact, more lightweight, and thinner, as the electronic devices become more compact, more lightweight, and, and thinner.
Various shapes of heat pipes are known as cooling devices. For example, Patent Literature 1 discloses a structure in which a heat pipe having a circular cross-section is fixed by metal fittings on a metal plate, and the shape of a heat receiving portion is modified as a plane which is brought into contact with the metal plate. Patent Literature 2, for example, discloses a heat pipe (container) in which many cavities are formed, and a wick and a working liquid are enclosed therein. Screw-fastening holes are formed at portions of the heat pipe, through which springs or screws are fitted to fix the heat pipe on a substrate, while the heat pipe is pressed against a heat-generating body placed on the substrate. Patent Literature 3, for example, discloses a structure in which thin foil-like sheets made by different types of thermal refining are bonded together to provide a flexible container in which a wick and a working liquid are enclosed. Such a structure is provided as a flexible heat pipe structure (sheet-like heat pipe) which allows smooth thermal connections, even if there is a height gap between a heat-generating element and a heat sink.